Extended interaction resonant electric discharge system



Aug. 30, 1966 N. T, I Avoo 3270,24@

EXTENDED INTERAGTION RESONANT ELECTRIC DISCHARGE SYSTEM Filed DSC. 13, 1961 His Attorney United States Patent O 3,270,240 EXTENDED INTERACTION RESONANI ELECTRIC DISCHARGE SYSTEM Norman T. Lavoo, Watervliet, N.Y., assigner to General Electric Company, a corporation of New York Filed Dec. 13, 1961, Ser. No. 159,004 Claims. (Cl. 315-3) The present invention relates to improved electron beam discharge devices and more particularly to improved eX- tended interaction resonant electric -discharge systems.

The continued development of systems employing electrica'l discharge devices has imposed continually increasin-g requirements on the performance capabilities of the device. There has been a need for higher output powers at higher frequencies, at better efficiencies, over wider band widths and the like. The selection of a particular type of discharge device has in general involved a compromise on t-he capabilities of a particular tube with respeot to at least some of these requirements. In a-n attempt to obtain reasonably good efliciency overa substantial band width in 'high power, high frequency devices, tubes employing .an extended interaction with an electron beam by means of a res-onant structure of extended length `along fthe beam have been proposed. A device of this character is shown and claimed, for example, in Patent 2,-888,600-Rich, in which a resonant structure involving a slow wave structure such `as `a helix, is coupled with ya conducting structure through a region of high strength electric ield, both along the helix .and in the surrounding conducting structure so that the structure as a whole may be tuned by a tuning cavity. In McArthur Patent No. 2,860,280, dated November 11, 1958, is described and claimed an electric discharge device of this type in which the resonant structures including the resonant slow wave structure, replace the resonant cavities of a velocity modlulation tube or klystron. The present invention involves `an improved structural arrangement of the slow wave structure and surrounding conducting structure which are coupled together to provide the extended interaction resonant structure particularly `suitable for devices of tthe velocity modulation type and which also provides improved means for stabilizing the operation of the resonant structures in the desired mode.

In accordance with the illustrated embodiment of .the invention, a velocity modulation device having three extended interaction resonant structures is provided with each structure including a slow wave structure, specifically a helix coupled to Ia surrounding cavity through a coupling gap provided between two apertured and opposed hemispherical `shielding members near the center of the helix. The surrounding conducting structure may be tuned by means of suitable plungers and the operation of each of the interaction structures is stabilized in the desired mode by means of an electrically lossy member or structure closely coupled to the Iiield of the extended interaction structure at ,a region of low longitudinal electric field in the desired mode. At undesired modes a substantial electric 4field exists at these locations and these modes are, therefore, `attenuated While at the desired mode .the `longitudinal electric field is essentially Zero at the location of these energy absorbing members and at- .tenuation is minimized. It has been found that the operation niay be stabilized in this manner over a significant frequency range and without substantial loss of energy at the desired frequency of operation. It is ,accordingly an important object of the present invention to provide an improved extended interaction resonant type of electric discharge system, particularly with respect to an improved coupling between the slow wave structure `and the conducting structure associated therewith to provide the res- Patented August 30, 1966 onant structure and to improved stabilization of such systems in the desired mode of operation.

Further objects and advantages of .the present invention will become apparent as the following description proceeds, reference being had to the accompanying drawing and its scope will be pointed out in the appended claims.

yIn the drawing:

FIG. 1 is an elevational view, partly in section, of an electric discharge device embodying my invention;

FIG. 2 is an enlarged elevational view, partially broken aw-ay, showing one of the extended interaction structures of the device of FIG. l;

FIG. 3 is a View taken along the line 3 3 of FIG. 2;

FIG. 4 is an enlarged View of a portion of the structure of FIG. 2 showing particularly the energy 4absorbing means coupled to the extended interaction structure;

FIG. 5 is an enlarged view of one end of the extended interaction structure -showing the movable mounting;

PIG. 6 is an enlarged sectional view taken along line 6 6 of FIG. 2 and showing a detail of the helix cooling structure; and

FIG. 7 is an enlarged sectional View through the closed end of the helix.

Referring now to the drawing, .the present invention is shown embodied in an elect-ric discharge device of the beam type in which Ia beam produced by an electron gun structure designated generally lby the numeral 10 is.accelerated to a 'hollow cylindrical collector electrode 11 and along its path intermediate to the lgun and collector passes through three regions of interaction with conducting structures 1-2, 13 and `14 corresponding generally to the three cavities of the three-cavity velocity modulation tube but embodying extended interaction structures of the present invention. As lbest shown in FIG. 2, each region of interaction comprises an extended slow wave structure such as .a helix 15 supported from tunnel-like members 17 and 1'8 which vare formed integrally with or bonded to a pair of spaced metallic disk-.like terminals 19 and 20, respectively, which are hermetioally sealed in `axially spaced and insulated relation by a cylindrical ceramic insulator 21. As illustrated, one end of the helix 15 is bonded directly to the tunnel `17 while the other end is provided with a sleeve or collar 22 which is slidably received on an extension 23 of the tunnel .18 with an interposed dielectric sleeve 24 which capacitively couples the helix to the Itunnel 118, and as a result, to the terminal 20 as shown in particular in FIG. 5. This arrangement for supporting one end of the helix 1S simplifies what would otherwise 'be a very diicult task of assembling and fabricating the envelope and interaction structures.

As is also apparent from the left-hand portion of FIG. 2 and .the enlarged section view of FIG. 6, the end of the helix which is supported from the tunnel 1.9 is hollow and communicates with the exterior of the disk-like member 19 through an extension 15. A smaller diameter centrally located conduit 1'5 extends through the helix and as shown in FIG. 7, .terminates short of the righthand end of the helix 15 and is cut at an acute angle to assure that the passage is open. This permits Ia cooling Huid, such as water, to iiow through the helix 15 which is particularly important in connection with .the output section of the tube shown at 14. Similar cooling arrangements may be provided for 'both sections `13` and 1'4. In the construction shown the resonators forming a part of the extended interaction structures are of the external type and only one has been illustrated. This is shown in connection with the input interaction structure 12- and as illustrated includes a two-part generally rectangular resonator 25 lwhich is clamped about the discharge device in engagement with the terminals 1-9 and 20 and held in position by suitable holding means, such as screws 26. The common longitudinal electric fields of the resonator and the helix merge in a region of strong fields provided between the apertured 4hemispherical shielding members 27 and 28 supported respectively from the terminalst19 and 20 and terminating in spaced relation in close proximity to the interior of the helix to provide a coupling gap -at 29.

The resonator 21S may be closed at its ends by end Walls 30 and 31 and the electrical ends of the resonator provided by plungers -32` adjustably mounted from end walls 30 and 311 by suitable threaded members 33 and cooperating adjusting nuts 34. The engagement of the plungers with the inner walls of the resonator is provided by 4the conducting spring fingers 3S.

With such an arrangement the resonator including the enclosing conducting structure, the shields 27 and 28 and the helix 219 may be tuned by means of the plungers so that a standingwave one wavelength long is produced along the helix in the operation of the device at the desired frequency. The longitudinal electrical field is -a maximum at the center of .the lhelix at the gap 29 and in accordance with -an important feature of the present invention, operation in this mode may be stabilized by providing an electrical lossy member spaced from the gap 29 along the length of the helix and at a region of low longitudinal electric field for the wanted frequency. As illustrated in FIG. 2, the member 36 is supported between the second and third turns of a ten turn helix. As more clearly seen in the enlarged view of FIG. 4, the member '36 may be in the form of ceramic member 37 having a thin metallized coating 38 on the surface thereof facing the helix and bonded at its ends to conducting clip members 39 which engage and may be bonded to the helix 1S. Ceramic members 40 may be bonded to lthe members 3-9 opposite the member 38 to provide a relatively strain-free seal in accordance with known practices in the sealing art. It will be apparent that the loading provided by the assembly 36 may be controlled by both its area and the thickness of the metallic coating applied. It will `also be -appreciated that a similar element may be provided at the other side of the center of the helix approximately half way between the center and the end thereof.

It will be readily apparent to those skilled in the art that the half way location between the center and the end of the helix will provide maximum attenuation for the second harmonic and a minimum attenuation at the desired frequency. The position of the helix may be adjusted somewhat to improve attenuation of other unwanted frequencies but it must be appreciated that such movement will tend to increase the loss Iat the desired frequency.

In FIG. 3 is illustrated an input coupling for supplying input energy to lthe device of FIG. `1. As shown in FIG. 3 this coupling may be in the form of a concentric transmission line having an outer conductor il and a central conductor 42 terminating in Ia loop 43 extending into proximity with the cylindrical insulator 21 of the discharge device and having the end bonded to the inner end of the outer conductor 41 as at 44. The central conductor may be positioned and supported by a suitable insulating disk 45. -In accordance with the preferred embodiment illustrated, the outer conductor 4l1 of the transmission line is supported within a holding fiange 46 which permits rotation of the concentric line assembly and adjustment of 4the angular position and degree of coupling of the coupling loop 43. Suitable contact fingers l47 may be provided on the outer Wall of the outer conductor 41 at its inner end in order to engage cond-uctively the wall of the resonator.

In the foregoing detailed description, a single extended resonant interaction structure for an electric discharge device one unit, namely the input unit, corresponding to resonant structure 12 of the device of FIG. 1 has been described. It will be apparent that similar structures are provided at 13 and 14. The input structure accomplishes the function of the input resonator of a three cavity klystron, for example, but the interaction with the electron beam takes place over the length of the resonant helix or in the particular embodiment illustrated, one full wave of the standing electromagnetic wave. The intermediate structure at 13 corresponds to the idler cavity of a three cavity klystron and enhances the bunching of the electrons modulated by the input structure. This structure may be tuned to a slightly different frequency if desired in accordance with the stagger tuned technique employed in three cavity klystrons. It will be appreciated that the resonant structure is essentially the same as that described in connection with the detailed descrip-tion of the structure y12 and that the attenuating elements 38 may be employed. The output resonant structure is of similar construction and will include an output coupling loop similar .to that described in connection with the input resonant structure 12.

As will be apparent from the drawing, the gap between the hemispherical shielding members 27 and 28 in the output section of the tube 14 is substantially twice that illustrated in connection with the sections 12 and 13. This increased gap provides for the greater coupling between the fields of the helix and of the resonator required in the output section 14 of the device.

The beam of focused electrons is provided by the electron gun structure 1t) which may include an electron emitting cathode 49 and a focusing and shield electrode 50 having an inwardly directed flange 51. The shield is supported from an envelope structure by an externally accessible terminal 52. The cathode and one terminal of the heater element (not shown) is supported and electrically connected to a terminal 53 and the other terminal of the heater is connected with a terminal 54.

In operation, the collector and conducting structures of the various resonant structures may be maintained at ground potential and the cathode terminal 53 maintained at a high negative voltage by a battery 55. The focusing cylinder may be maintained at a voltage negative with respect to the cathode by a suitable amount such as 200 volts, for example, by a conductor 56 connected to battery 55 and the heater may be energized by a voltage obtained between the cathode connection and a heater supply conductor 57. As will be readily understood, a collimating magnetic field may also be utilized to collimate the beam as it traverses the path between the electron gun structure and the collector 11. It will be appreciated that the device described in connection with FIG. l and the resonators associated with structures 13 and 14, as indicated, that high frequency energy supplied to the input transmission line and coupled to the resonant structure by the coupling 43 will serve to velocity modulate the beam as a result `of the interaction with the standing wave produced along the helix and that this bunching will be enhanced in the intermediate resonator associated with structure 13. The interaction between the output resonant structure and the electron beam likewise takes place over an extended length which has one complete wavelength `of the standing wave produced in the structure 14 andenergy extracted from the resonant structure by means of an output coupling corresponding generally to the input coupling described in connection with the resonant structure 12.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical discharge device comprising means for establishing an electron beam along a predetermined path 5 and a resonant structure along said path for interacting with said beam including an elongated helical slow wave `structure surrounding said path and a hollow conductive `structure surrounding and cooperating with said helical slow wave structure to provide a structure resonant at an operating frequency, said conductive structure including means shielding the interior of said hollow conductive `structure from the longitudinal electric field associated with said helical slow wave structure except for a limited length thereof in a region of high longitudinal electric field at the operating frequency and means coupled to the exterior of said helical slow wave structure and spaced dongitudinally from said limited length thereof at a region of low longitudinal electric field at said operating frequency to enhance the dissipation of energy at frequencies other than said operating frequency.

2. An electrical discharge device comprising means for establishing an electron beam along a predetermined path and a resonant structure along said path for interacting with said beam including an elongated helical slow wave `structure surrounding said path and a hollow conductive structure surrounding and cooperating with said helical slow wave structure to provide a structure resonant at an operating frequency, said conductive structure including a pair of apertured hemispherical shielding members shielding the interior of said hollow conductive structure from the longitudinal electric lield associated with said helical slow wave structure and having the adjacent portion thereof spaced to couple a limited length of said helical slow wave structures in a region of high longitudial electric eld at the operating frequency with the interior of said conductive structure and means providing high electrical loss adjacent said helical slow wave structure between said length thereof and one end thereof.

3. An extended interaction structure for a beam type electric discharge device comprising a pair of spaced conducting walls, a conductive slow wave structure extending between said walls and fixedly attached to one of said Walls, the other of said Walls providing longitudinally extending support for the other end of said slow wave structure to permit relative movement between said slow wave structure and said other of said end walls in the direction of the spacing of said end walls, and means hermetically sealing said end walls in insulated relation.

4. An extended interaction structure for a beam type electric discharge device comprising a pair of spaced apertured conducting walls, a hollow conductive slow wave structure extending between said Walls and xedly attached to one of said walls in alignment with the aperture therein, the other of said walls providing longitudin nally extending support surrounding the aperture therein for the other end of said slow wave stnucture to permit relative movement between said slow wave structure and said other of said end walls in the direction of the spacing of said end walls, means capacitively connecting said slow wave structure with said other end wall, and means sealing said end walls together in spaced insulated relation.

5. An extended interaction structure for a beam type electric discharge device comprising a pair of spaced apertured conducting walls, a helical slow wave structure extending between said walls and fixedly attached to one of said walls in alignment with the aperture therein, a hol-low hub extending inwardy from the `other of said walls providing longitudinally extending support for the other end of said helix to permit relative movement between said slow wave structure and said other of said end walls in the direction of the spacing of said end walls, an insulating spacer between said hub and said helix, and means sealing said end walls together in spaced insulated relation.

References Cited by the Examiner UNITED STATES PATENTS 2,647,219 7/1953 Touraton et al. S15-5.39 X 2,888,600 5/1959 Rich 315-53 2,945,155 7/1960 Chodorow 315-539 3,050,657 8/1962 Branch 315--3.6 3,192,430 6/1965 Chodorow 315-3.5

HERMAN KARL SAALBACH, Primary Examiner. ARTHUR GAUSS, Examiner.

S. CHATMON, I R., Assistant Examiner. 

1. AN ELECTRICAL DISCHARGE DEVICE COMPRISING MEANS FOR ESTABLISHING AN ELECTRON BEAM ALONG A PREDETERMINED PATH AND A RESONANT STRUCTURE ALONG SAID PATH FOR INTERACTING WITH SAID BEAM INCLUDING AN ELONGATED HELICAL SLOW WAVE STRUCTURE SURROUNDING SAID PATH AND A HOLLOW CONDUCTIVE STRUCTURE SURROUNDING AND COOPERATING WITH SAID HELICAL SLOW WAVE STRUCTURE TO PROVIDE A STRUCTURE RESONANT AT AN OPERATING FREQUENCY, SAID CONDUCTIVE STRUCTURE INCLUDING MEANS SHIELDING THE INTERIOR OF SAID HOLLOW CONDUCTIVE STRUCTURE FROM THE LONGITUDINAL ELECTRIC FIELD ASSOCIATED WITH SAID HELICAL SLOW WAVE STRUCTURE EXCEPT FOR A LIMITED LENGTH THEREOF IN A REGION OF HIGH LONGITUDINAL ELECTRIC FIELD AT THE OPERATING FREQUENCY AND MEANS COUPLED TO THE EXTERIOR OF SAID HELICAL SLOW WAVE STRUCTURE AND SPACED LONGITUDINALLY FROM SAID LIMITED LENGTH THEREOF AT A REGION OF LOW LONGITUDINAL ELECTRIC FIELD AT SAID OPERATING FREQUENCY TO ENHANCE THE DISSIPATION OF ENERGY AT FREQUENCIES OTHER THAN SAID OPERATING FREQUENCY. 